The following relates generally to wireless communication, and more specifically to systems and methods to identify and optimize ZeroCorrelationZoneConfig (Ncs) parameter and logical root sequence assignments. Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple mobile devices. Base stations may communicate with mobile devices on downstream and upstream links. Each base station has a coverage range, which may be referred to as the coverage area of the cell. At power-on, or after a long standby time, a mobile device may not be synchronized with the base station. To achieve synchronization, the mobile device may carry out a Random Access (RA) procedure with the base station. In order to distinguish between different mobile devices performing an RA procedure, different preambles may be transmitted by different mobile stations to request access to the base station. Preamble structures may have a certain level of orthogonality to distinguish between different users. Such preambles may be derived from cyclic sequences. Different preambles may be derived from a same base sequence by introducing cyclic shifts or different preambles may be derived from different base sequences. A base station may have one or more base sequences assigned to it along with an allowed cyclic shift. The Ncs parameter indicates the amount of cyclic shift of the root sequence (or base sequence) to provide orthogonality between different preambles generated from each shift of the root sequence. Different roots (or groups of roots) may be assigned to different base stations so that preambles generated by devices in the coverage area of one base station are not detected by another base station. Moreover, a minimum physical distance should be secured before reusing the same root sequences at another base station. The physical distance should be far enough to allow attenuation for possible users performing random access channel (RACH) procedures with their serving base station.
Planning the use of root sequences in networks is a non-trivial task. This planning may be assisted by implementing Self-Optimizing Network (SON) features to allow the optimum values for certain parameters to be derived based on actual measurements. The number of root sequences used by a base station should be minimized to allow for larger reuse distance, (i.e., the distance between base stations that use the same root sequences may be increased). However, reducing the number of root sequences used by a base station implies reducing the length of the cyclic shift (i.e., reducing the Ncs parameter). The length of the cyclic shift depends on the size of the cell of the base station and it cannot be reduced too much.